Parts of the brain may look younger after a stroke, suggesting the brain can reorganise itself to help make up for damage.
Scientists analysed brain scans from more than 500 stroke survivors collected across 34 research centres in eight countries.
Using deep learning trained on tens of thousands of MRI scans, they estimated the biological age of different regions in each half of the brain and looked at how stroke affects structure and recovery.
They found that people with severe physical impairments after a stroke showed signs of a “younger” brain structure in areas that were not damaged.
The pattern suggests the brain may be adapting and reorganising after injury.
The research was carried out by the USC Mark and Mary Stevens Neuroimaging and Informatics Institute as part of the ENIGMA Stroke Recovery Working Group, a global collaboration combining data from more than 50 countries.
“We found that larger strokes accelerate ageing in the damaged hemisphere but paradoxically make the opposite side of the brain appear younger,” said Hosung Kim, associate professor of research neurology at the Keck School of Medicine of USC and co-senior author of the study.
“This pattern suggests the brain may be reorganising itself, essentially rejuvenating undamaged networks to compensate for lost function.”
To carry out the analysis, researchers used a graph convolutional network, a type of artificial intelligence.
It estimated the biological age of 18 brain regions using MRI data and compared that with each person’s actual age, a measure known as brain-predicted age difference, or brain-PAD, which can indicate brain health.
When brain age measurements were compared with motor function scores, a clear pattern emerged. Survivors with severe movement impairments, even after more than six months of rehabilitation, showed younger-than-expected brain age in regions opposite the injury site.
This effect was especially strong in the frontoparietal network, a group of brain regions involved in movement planning, attention and coordination.
“These findings suggest that when stroke damage leads to greater movement loss, undamaged regions on the opposite side of the brain may adapt to help compensate,” Kim explained.
“We saw this in the contralesional frontoparietal network, which showed a more ‘youthful’ pattern and is known to support motor planning, attention, and coordination.
“Rather than indicating full recovery of movement, this pattern may reflect the brain’s attempt to adjust when the damaged motor system can no longer function normally.
“This gives us a new way to see neuroplasticity that traditional imaging could not capture.”
By standardising MRI data and clinical information from many research groups, the team created what it described as the largest stroke neuroimaging dataset of its kind.
Arthur W. Toga, director of the Stevens INI, said the scale of the dataset was key to spotting subtle patterns.
He said: “By pooling data from hundreds of stroke survivors worldwide and applying cutting-edge AI, we can detect subtle patterns of brain reorganisation that would be invisible in smaller studies.
“These findings of regionally differential brain ageing in chronic stroke could eventually guide personalised rehabilitation strategies.”
The researchers plan to continue the work by following patients over time, from the early stages after a stroke through long-term recovery.
They said tracking how brain ageing patterns and structural changes evolve could help doctors tailor treatment to each person’s recovery, with the aim of improving outcomes and quality of life.
